SEARCH · PubMed Health

Results for “NUCLEOTIDASES”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources

PubMed1985

Membrane-bound 5'-nucleotidase in marine luminous bacteria: biochemical and immunological properties.

A novel 5'-nucleotidase previously described in halophilic Vibrio costicola was detected in marine Vibrio and Photobacterium strains. The enzyme of marine bacteria was similar in its properties to the 5'-nucleotidase of Vibrio costicola; it was outwardly oriented in the cytoplasmic membrane and dephosphorylated nucleoside 5'-tri-, di-, and mono-phosphates to respective nucleosides before uptake. The enzyme in marine strains was immunologically cross-reactive with the antibody raised against the purified 5'-nucleotidase of Vibrio costicola. The uptake of the products of ATP hydrolysis was studied in Vibrio harveyi, and it was shown that both adenosine and inorganic phosphate released upon the action of 5'-nucleotidase were rapidly taken up by the cell.

5'-Nucleotidase↗

PubMed1983

Partial purification and zinc dependence of human red cell pyrimidine-5'-nucleotidase.

Human red cell pyrimidine-5'-nucleotidase (EC 3.1.3.5) was partially purified from the blood of normal subjects by ion-exchange and affinity chromatography. Red cells were lysed in 50 mmol/l Tris-Cl buffer at pH 7.5 containing 1.0 mmol/l dithiothreitol and 0.5 mmol/l EDTA. The lysate was centrifuged and introduced onto a column of Sephadex A-50. After washing, the pyrimidine-5'-nucleotidase activity was eluted from the column with a NaCl gradient from 0 to 200 mmol/l in Tris buffer at pH 7.5. The pyrimidine-5'-nucleotidase was then desalted on Sephadex G-25 and introduced onto a UDP agarose column with a Tris buffer at pH 6.5 containing 150 mmol/l NaCl. This partial purification resulted in an approximately 80,000-fold increase in enzyme concentration. The Km for the partially purified enzyme was 0.32 mmol/l for UMP, 0.16 mmol/l for CMP and 0.11 mmol/l for OMP with a pH maximum of 7.5. This partially purified pyrimidine-5'-nucleotidase was then dialyzed in 50 mmol/l Tris-Cl buffer at pH 7.5 with 0.01 mmol/l CaCl2 and NaCl against 2 X 10(-3) mol/l 1,10-phenanthroline for 24 h at 4 degrees C. This incubation resulted in 73% decrease in enzyme activity which could be restored by the addition of zinc into the mixture, but not by the addition of other divalent metal ions.

5'-Nucleotidase↗

PubMed1985

Cytochemical localization of 5'-nucleotidase in the frog (Rana pipiens) retina. A histochemical and cytochemical study.

Localization of 5'-nucleotidase in the frog retina was investigated using histochemical and cytochemical techniques. Light-microscopic observations revealed the presence of this enzyme in the inner retinal layers (the nerve fiber layer, ganglion cell layer, and inner plexiform layer). Ultrastructural investigations revealed that the enzyme activity is associated with the plasma membranes of the Müller cell processes, whereas the Müller cell processes present in the outer retinal layers did not demonstrate any detectable enzyme activity. This observation would appear to confirm our previous findings, that 5'-nucleotidase is an ectoenzyme, but its distribution in frog retina differs from that in rodents and it is only present in the inner layers of the retina. The prominent localization of 5'-nucleotidase on the glial plasma membrane may be viewed in the context of the widely accepted interaction between neurones and glial cells. Since nucleotides do not penetrate the plasma membrane, a mechanism to produce membrane-permeable adenosine, important for neuronal function, is postulated. It is known that 5'-nucleotidase produces adenosine by hydrolyzing adenosine 5'-monophosphate (5'-AMP). Therefore one would expect that the glial membrane-bound enzyme can accomplish the final step in this mechanism by producing the adenosine in the extracellular spaces.

5'-Nucleotidase↗

PubMed1988

Erythrocyte pyrimidine 5'-nucleotidase and deoxynucleotidase isozymes: metallosensitivity and kinetics.

Erythrocytes from a subject with classical pyrimidine 5'-nucleotidase (P5N) deficiency (PND) possessed typically low nucleotidase activity with uridine 5'-monophosphate (UMP) and cytidine 5'-monophosphate (CMP) as the substrates with subnormal dephosphorylation of 2'-deoxy thymidine 5'-monophosphate (dTMP) and 2'-deoxyuridine 5'-monophosphate (dUMP) and intermediate activity with 2'-deoxycytidine 5'-monophosphate (dCMP). Contrary to previously reported data, there was enzyme activity with all five substrates. The metallosensitivities of the P5N isozymes using UMP, dUMP, dCMP and dTMP as the substrates were defined. Nucleotidase (P5N) is slightly more sensitive than 2'-deoxy-pyrimidine 5'-nucleotidase (dP5N) to inhibition by lead, copper and mercury. Chromium stimulated more enzyme activity with dCMP than other substrates. Apparent Michaelis constants (Km) were calculated for UMP, CMP, dUMP, dCMP, and dTMP for PND and control subjects. Optimal activity was at pH 7.0-7.8 when using UMP and CMP as the substrates but at pH 5.5-6.5 with dUMP, dCMP and dTMP as the substrates. The Km, pH optima and metallosensitivities were, however, consistent with electrophoretic evidence for two and probably three isozymes: P5N with maximal affinity for UMP and CMP; dP5N with maximal affinity for dUMP and dTMP; and a closely related dCMPase. The relative activity with representative substrates can be used to distinguish homozygotes and heterozygotes for P5N deficiency and subjects with heavy metal exposure.

5'-Nucleotidase↗

PubMed1981

Plasma membrane enzymes in BALB/c lymphomas with either T or B cell properties, I. 5'-Nucleotidase.

Comparison of membrane bound 5'-nucleotidase activity has been made in crude extracts and plasma membrane fractions from Abelson virus transformed lymphomas, IgM, IgG and IgA producing plasmacytomas and from thymomas with different surface antigen markers. 5'Nucleotidase activity was characterised by the following criteria : 1) optimal pH for enzyme activity, 2) specificity of 5'AMP as a substrate at the optimal pH, 3) specific inhibition of the enzyme by alpha beta methylene ADP, 4) inhibition by EDTA. 5'-Nucleotidase was found to be present on the following B cells : Abelson virus transformed lymphomas, plasmacytomas and LPS-stimulated blasts from nu/nu spleens. The enzyme was also found in one thymoma Lut 13, but it was absent from all the other thymomas studied. A possible relationship between 5'-Nucleotidase and purine metabolism in lymphocyte subpopulations is suggested by the results.

5'-Nucleotidase↗

PubMed1983

Biological variation of rabbit chondrocyte 5'nucleotidase.

The activity of 5'nucleotidase was investigated in rabbit chondrocytes. Studies of chondrocytes in organ culture and intact cells revealed that ecto-5'nucleotidase activity varies with the age of the animal. Specific activities of 0.29, 0.62, 1.97, and 1.39 mumole/hr/10(6) cells were observed in intact cells from 3-week-, 3-month-, 6-month-, and 2-year-old animals. Specific activities of 15.5, 33.1, 80.3, and 39.5 mumole/hr/mg protein, respectively, were observed when the enzyme protein was solubilized from disrupted cells with the detergent octyl-beta-D-glucopyranoside. Membrane-bound nonspecific neutral phosphatase activity did not vary with age. Activity of 5'nucleotidase was observed on all chondrocytes using a histochemical staining technique. Kinetic properties of the enzyme from animals of different ages were investigated. No differences were noted in apparent Km value for AMP (23 microM), pH optima (7.3), substrate competition studies, and effects of MgCl2 or CaCl2. These data demonstrate a biological variation in rabbit chondrocyte 5'nucleotidase activity with age. The variation of activity represents an apparent increase in the amount of enzyme protein rather than an alteration in kinetic properties.

5'-Nucleotidase↗

PubMed1989

Phosphorylation of 2',3'-dideoxyinosine by cytosolic 5'-nucleotidase of human lymphoid cells.

2',3'-Dideoxyinosine (ddlno) is a potent and selective inhibitor of human immunodeficiency virus in human lymphoid cells and monocytes/macrophages. Earlier studies [J. Biol. Chem. 263:15354 (1988)] showed that anabolism of ddlno in human lymphoid cells is mediated via an initial step of phosphorylation and subsequent amination to dideoxy-AMP via adenylosuccinate synthetase/lyase. Evidence was obtained that neither adenosine kinase nor deoxycytidine kinase is involved in the phosphorylation of this compound in human lymphoid cells. We now find that, in the presence of MgCl2, KCl, and inosine-5'-monophosphate as phosphate donor, purified cytosolic 5'-nucleotidase catalyzed the phosphorylation of ddlno. Although not phosphate donors, ATP, diadenosine tetraphosphate, and glycerate-2,3-bisphosphate stimulate this phosphorylation by the nucleotidase 4-5-fold. In addition to ddlno, the antiviral nucleoside analogs 2',3'-dideoxyguanosine and carbovir were substrates for this enzyme. The relative phosphorylation of these compounds varied with the concentration of the phosphate donor IMP. Approximate Km values of the nucleotidase for inosine, ddlno, dideoxyguanosine, and carbovir were, respectively, 3.4, 0.5, 0.9, and 1.7 mM. Although the substrate activity of dideoxynucleosides is inefficient, it appears likely that this nucleotidase is responsible for the metabolism of these compounds to their active nucleotides, yielding antiviral activity in human lymphoid cells.

5'-Nucleotidase↗

PubMed1988

High Km soluble 5'-nucleotidase from human placenta. Properties and allosteric regulation by IMP and ATP.

A human placental soluble "high Km" 5'-nucleotidase has been separated from "low Km" 5'-nucleotidase and nonspecific phosphatase by AMP-Sepharose affinity chromatography. The enzyme was purified 8000-fold to a specific activity of 25.6 mumol/min/mg. The subunit molecular mass is 53 kDa, and the native molecular mass is 210 kDa, suggesting a tetrameric structure. Soluble high Km 5'-nucleotidase is most active with IMP and GMP and their deoxy derivatives. IMP is hydrolyzed 15 times faster than AMP. The enzyme has a virtually absolute requirement for magnesium ions and is regulated by them. Purine nucleoside 5'-triphosphates strongly activate the enzyme with the potency order dATP greater than ATP greater than GTP. 2,3-Diphosphoglycerate activates the enzyme as potently as ATP. Three millimolar ATP decreased the Km for IMP from 0.33 to 0.09 mM and increased the Vmax 12-fold. ATP activation was modified by the IMP concentration. At 20 microM IMP the ATP-dependent activation curve was sigmoidal, while at 2 mM IMP it was hyperbolic. The A0.5 values for ATP were 2.26 and 0.70 mM, and the relative maximal velocities were 32.9 and 126.0 nmol/min, respectively. Inorganic phosphate shifts the hyperbolic substrate velocity relationship for IMP to a sigmoidal one. With physiological concentrations of cofactors (3 mM ATP, 1-4 mM Pi, 150 mM KCl) at pH 7.4, the enzyme is 25-35 times more active toward 100 microM IMP than 100 microM AMP. These data show that: (a) soluble human placental high Km 5'-nucleotidase coexists in human placenta with the low Km enzyme; (b) under physiological conditions the enzyme favors the hydrolysis of IMP and is critically regulated by IMP, ATP, and Pi levels; and (c) kinetic properties of ATP and IMP are each modified by the other compound suggesting complex interaction of the associated binding sites.

5'-Nucleotidase↗

PubMed1985

Isolation of 5'-nucleotidase from chicken gizzard, its properties, and subcellular localization in chicken tissues using monospecific antibodies.

After solubilization with zwitterionic detergents 5'-nucleotidase was purified to homogeneity from chicken gizzard. Purified 5'-nucleotidase appeared to be composed of a single polypeptide chain of 79 kDa as revealed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE); gel filtration studies in the presence of detergents, however, indicated that the native enzyme is a homodimer. Antisera against purified chicken gizzard 5'-nucleotidase were raised in rabbits, they were shown to inhibit the enzymic activity of different 5'-nucleotidase preparations in a species and tissue specific manner. On frozen sections the antisera stained the cell periphery of chicken gizzard smooth and skeletal muscle and faintly stained cardiac muscle cells when using the indirect immunofluorescent technique. In chicken cardiac tissue, a prominent staining of the vascular system also became apparent. In avian and rat non-muscle tissues (hepatic and pancreatic tissue) the vascular system was always found to be brightly stained, i.e. the vascular smooth muscle and endothelial cells. On frozen sections of chicken liver the sinusoidal region of the hepatocytes was brightly stained, the bile canalicular region, however, only faintly. Using the immunocytochemical technique, a more prominent tissue specificity rather than species specificity of the available antisera became apparent. This may therefore reflect the existence of tissue-specific isoforms of the enzyme.

5'-Nucleotidase↗

PubMed1985

Isozymes of human erythrocyte pyrimidine 5'-nucleotidase.

A scheme for the partial purification of human erythrocyte pyrimidine nucleotidase isozymes is presented. The characteristics of three of these were distinctively established. One isozyme, designated pyrimidine nucleotidase (PyrNase), is active for uridine monophosphate (UMP) and cytidine monophosphate (CMP), but not for thymidine monophosphate (dTMP). Two other isozymes, designated thymidine nucleotidase I (ThyNase I) and thymidine nucleotidase II (ThyNase II), were active for dTMP, but less so for UMP and CMP. Molecular weights of PyrNase, ThyNase I, and ThyNase II were estimated as 52,000, 52,000, and 48,000, respectively. Isoelectric points of these isozymes were 5.22, 4.90, and 4.68, respectively. Kinetic study revealed that the Km value for dTMP of ThyNase I was 3.83 mmol/L and of ThyNase II was 6.26 mmol/L.

5'-Nucleotidase↗

PubMed1985

A B-cell hybridoma product inhibiting antibody secretion via 5'-nucleotidase.

A mouse spleen cell/plasmacytoma fusion designed to generate hybridomas making monoclonal antibodies to human lymphocyte 5'-nucleotidase yielded three hybridomas secreting material which inhibited about 50% of human and mouse lymphocyte ecto 5'-nucleotidase activity. The inhibition proved not to be due to antibody but to material of molecular weight 44,000 +/- 7,000 which was not part of an immunoglobulin molecule, although it may be related to a B cell Fc gamma receptor. In a haemolytic plaque assay this material inhibited the production of IgG but not IgM antibody by spleen cells of mice immunized with dinitrophenylated keyhole limpit haemocyanin. By contrast, IgG production by pokeweed mitogen-stimulated human tonsillar lymphocytes (assessed by reverse haemolytic plaque assay) was partially inhibited only by ascitic fluid of one of the hybridomas. The factor was called BAN (B cell anti 5'-nucleotidase). The suppressive action of BAN on IgG production was blocked by antibodies against 5'-nucleotidase suggesting that the lymphocyte enzyme may be acting as a BAN receptor.

5'-Nucleotidase↗

PubMed1986

Biosynthesis and intracellular transport of rat liver 5'-nucleotidase.

To investigate biosynthesis and intracellular transport of 5'-nucleotidase, we purified this enzyme from rat liver and prepared antibodies. In immunoblot analysis, 5'-nucleotidase from the plasmalemmal, Golgi, and tritosomal fractions migrated as a single band of 72 kDa. The immunoreactive 68-kDa band was detected in the rough microsomal fraction and only the 72-kDa polypeptide contained sialic acids. The single polypeptide of 61 kDa immunoprecipitated from the translation products with the membrane-bound polysomal RNAs by the cell-free system converted to the 68-kDa form associated with membranes, when translated in the presence of microsomal vesicles. 5'-Nucleotidase from cultured primary hepatocytes pulse-labeled with [35S]methionine for 20 min migrated as a 68-kDa polypeptide. Within 45 min of chase, the 68-kDa form was converted to the 72-kDa form. Upon treatment with tunicamycin, a new immunoreactive polypeptide of 59 kDa was obtained. These results suggest that 5'-nucleotidase is translated on the membrane-bound polysomes as a 61-kDa precursor and that the cleavage of the 2-kDa signal peptide and the core glycosylation co-translationally convert the precursor to the 68-kDa form, which is subsequently processed in the Golgi complex to the 72-kDa form.

5'-Nucleotidase↗

PubMed1986

Role of 5'-nucleotidase in adenosine-mediated renal vasoconstriction during hypoxia.

Regulation of renal function by endogenous adenosine production was examined in isolated perfused rat kidneys. Reducing perfusate pO2 from 400 +/- 15 to 130 +/- 5 mm Hg for 20 min created an energy deficit and increased adenosine in venous perfusate (0.06 +/- 0.02 to 0.79 +/- 0.15 microM) and snap-frozen renal cortex (5.6 +/- 1.4 to 16.7 +/- 2.7 nmol/g wet wt.). A competitive inhibitor of 5'-nucleotidase, alpha,beta-methyleneadenosine diphosphate (120 microM), inhibited the production of adenosine during hypoxia (perfusate, 0.26 +/- 0.05 microM and renal cortex, 3.1 nmol/g) but did not prevent the decline in cortical tissue ATP and ADP. The inhibitor was concentrated 3-fold in renal cortex compared to perfusate and could therefore inhibit both ecto and endo 5' nucleotidases. Vascular resistance increased 11.1 +/- 0.5% during hypoxia. Inhibition of 5'-nucleotidase reduced the vasoconstrictive response by 40% (P less than .01). An A1 antagonist, 1,3-diprophyl-8-(2-amino-4-chlorophenyl)xanthine (10(-5) M), reduced the effect of hypoxia on vascular resistance by 60% (P less than .005). Adenosine deaminase (7-14 U/ml) added during hypoxia reduced venous adenosine from 1.0 to 0.3 microM and reduced vascular resistance by 3 +/- 1%. Neither the inhibitors nor adenosine deaminase significantly altered the response of glomerular filtration rate or sodium reabsorption to hypoxia. These results indicate that either ecto or endo 5'-nucleotidase controls the renal production of adenosine during an energy deficit and that endogenous adenosine constricts the renal vasculature.

5'-Nucleotidase↗

PubMed1984

Kinetic properties of 5' nucleotidase in blood lymphocytes from healthy subjects, immunodeficient patients and cord blood.

The Km for AMP for 5' nucleotidase was increased in lymphocytes from patients with common variable (CVH) and sex linked (XLH) hypogammaglobulinaemia and from patients with chronic lymphatic leukaemia (CLL): the Vmax of the latter was low. The kinetic constants for cord blood lymphocytes are similar to adults and the Km does not change with age in lymphocytes from healthy adults. alpha-beta-Methylene adenosine diphosphate competitively inhibited 5' nucleotidase in lymphocytes from both healthy subjects and patients with CVH: the inhibitor constant (Ki) was higher for lymphocytes from patients with CVH than from control subjects. The concentration of zinc, an activator and modulator of 5' nucleotidase, was similar in control and CVH lymphocytes. It is concluded that lymphocyte 5' nucleotidase is functionally, abnormal in both primary hypogammaglobulinaemia and CLL and is deficient in the latter. These results provide support for the concept that CVH is a stem cell disease.

5'-Nucleotidase↗

PubMed1980

Distributive patterns of 5'-nucleotidase and simple esterase in the diencephalon and mesencephalon of the garden lizard (Calotes versicolor).

Different enzymatic patterns of 5'-nucleotidase and simple esterase have been observed in the diencephalon and mesencephalon of the garden lizard, Calotes versicolor. Most of the brain centers have shown the enzyme activities, ranging from negligible through very strong, in the neurons and neuropil. However, two brain centers, the DLH and NM, were found negative to 5'-nucleotidase. On the other hand, no brain center showed negative picture in the preparations of simple esterase. In general, it has been observed that the enzyme activity dominates in the neurons than the neuropil both for 5'-nucleotidase and simple esterase. The major fiber tracts have shown mild reaction product of 5'-nucleotidase except a solitary fiber bundle, the lateral forebrain bundle, which demonstrated, invariably, strong to very strong enzyme activity; the commissura colliculi superioris was, however, negative for the enzyme activity. On contrary, most of the fiber tracts showed strong to very strong activity of simple esterase. The significance of the distributive patterns of the two enzymes in relation to various brain centers and fiber tracts has been discussed.

5'-Nucleotidase↗

PubMed1982

The activity of 5'-nucleotidase in liver plasma membranes is affected by the increase in bilayer fluidity achieved by anionic drugs but not by cationic drugs.

The 5'-nucleotidase activity of rat liver plasma membranes could be selectively modulated by the anionic drugs phenobarbital and pentobarbital, whereas the corresponding activity of a Lubrol-solubilized preparations remained unaltered. The perturbation in the outer half of the bilayer induced by phenobarbital, which lead to a depression in the high temperature onset of the lipid phase separation occurring in this half of the bilayer, concomitantly lowered the break temperature in Arrhenius plots of 5'-nucleotidase activity from 28 degrees C to 16 degrees C. The stimulation of the membrane-bound activity achieved by low anionic drug concentrations was attributed to a preferential fluidization of the outer half of the bilayer. Contrarily, the cationic drugs prilocaine and carbocaine, when tested over agent concentrations that dramatically increase the fluidity of the inner half of the bilayer, achieved no selective effects on the membrane-bound enzyme. Prilocaine (10 mM) was previously found to induce a lipid phase separation at 11 degrees C that was attributed to the lipids of the internal (cytosol-facing) half of the bilayer, but had no effect on the onset of the lipid phase separation occurring at 28 degrees C. Since Arrhenius plots of 5'-nucleotidase activity in the presence of 10 mM prilocaine concentrations demonstrated only the single break at 28 degrees C, we suggest that prilocaine is unable to selectively perturb the enzyme because this cationic drug preferentially interacts with the acidic phospholipids residing in the inner half of the bilayer. The activity of the ectoenzyme 5'-nucleotidase in rat liver plasma membranes appears to be regulated by the external half of the bilayer only. These results support the view that independent modulation of he fluidity or chemical constituents of each half of the bilayer can distinctly affect the activity of proteins that are themselves asymmetrically orientated within the bilayer.

5'-Nucleotidase↗

PubMed1982

Characterization of an adenosine 5'-triphosphate- and deoxyadenosine 5'-triphosphate-activated nucleotidase from human malignant lymphocytes.

The kinetic properties of a soluble, magnesium-dependent 5'-nucleotidase from human malignant lymphocytes have been determined. The partially purified enzyme is distinct from plasma membrane-associated 5'-nucleotidase and is free of nonspecific phosphatase activity. Among purine ribonucleotides, it reacted efficiently with inosine 5'-monophosphate and guanosine 5 -monophosphate and to a lesser degree with deoxyguanosine 5'-monophosphate. Adenosine 5'-monophosphate and deoxyadenosine 5'-monophosphate were 30-fold less efficient substrates. Increasing concentrations of adenosine 5'-triphosphate and deoxyadenosine 5'-triphosphate from 0 to 3 mM enhanced 5'-nucleotidase activity up to 7-fold. Guanosine 5'-triphosphate and deoxyguanosine 5'-triphosphate were much less effective enzyme activators, while uridine 5'-triphosphate was without effect. Inorganic phosphate inhibited dephosphorylating activity in both adenosine 5'-triphosphate-supplemented and unsupplemented buffer. The activation of this 5'-nucleotidase by deoxyadenosine 5'-triphosphate, combined with the relative inability of the enzyme to dephosphorylate deoxyadenosine 5'-monophosphate, conceivably may contribute to the adenine nucleotide degradation induced by deoxyadenosine in normal and malignant lymphocytes.

5'-Nucleotidase↗

PubMed1982

Effect of lead chelation therapy with EDTA in children on erythrocyte pyrimidine 5'-nucleotidase and with cytidine triphosphate levels.

Children with elevated whole blood lead levels were treated for 4 days with EDTA. Changes in whole blood lead concentrations, erythrocyte zinc protoporphyrin concentrations, red cell pyrimidine 5'-nucleotidase activities, and erythrocyte cytidine triphosphate (CTP) levels were measured during the course of the EDTA therapy. EDTA treatment decreased blood lead levels by approximately 50% after 4 days. An inverse relationship existed between blood lead levels and erythrocyte pyrimidine 5'-nucleotidase activity. Despite reactivation of pyrimidine 5'-nucleotidase enzyme activity by EDTA, there was no decrease in erythrocyte cytidine triphosphate or in zinc protoporphyrin concentrations. The lack of change in these two parameters during EDTA treatment supports the concept that pyrimidine 5'-nucleotidase inhibition by lead in the reticulocyte cytidine phosphate accumulation in moderate lead poisoning may reflect chronic lead overburden analogous to prolonged elevation of erythrocyte zinc protoporphyrins.

5'-Nucleotidase↗